1. Technical Field
This invention relates generally to linear motion assemblies, and more particularly to ball recirculation inserts therefor and assemblies therewith.
2. Related Art
Linear motion assemblies including recirculating balls, such as ball screw assemblies, for example, are used to effect linear actuation in various industries, such as machine tool, automotive, aircraft and aerospace, for example. Typically, a commercial ball screw assembly includes a screw with a continuous external helical ball groove and a ball nut with a continuous internal helical ball groove. The external helical ball groove of the ball screw and the internal helical ball groove of the ball nut are configured with substantially identical, continuous and uninterrupted leads (turns per inch). With the ball nut received coaxially and concentrically about the ball screw, the respective internal and external helical ball grooves are arranged in mirrored, opposite relation with one another in radially aligned relation, and a plurality of balls are disposed in a helical ball raceway formed between the aligned internal and external helical ball grooves.
Various ball return mechanisms are used to recirculate the balls, depending on the type of application. In some cases, a single ball return mechanism can be used to recirculate the balls over a single helical raceway, and in other cases, a plurality of ball return mechanisms can be used to recirculate the balls over a plurality of helical raceways. Where a plurality of helical raceways is formed, one type of ball return mechanism employed is commonly referred to as a crossover, button insert, or various combinations thereof. A crossover type insert, fixed with a recessed pocket of the ball nut, recirculates balls between immediately adjacent helical turns, such that the balls traverse a helical raceway for about 300-310 degrees, and are then recirculated over the remaining 60-50 degrees via the crossover insert. It is further known to provide the crossover inserts having a pair of oppositely extending curvilinear legs projecting laterally from a body of the crossover inserts, such that the legs curve away from the body to seat in a helical groove of the screw. The intended function of the legs is to come into play only during a failure scenario, such as if some or all of the balls were inadvertently fall out of the assembly. During such as failure, the legs are intended to serve as a backup sliding surface between the nut and screw to prevent freewheeling of the screw relative to the nut. During normal use, the legs are intended to remain in a clearance fit, in their entirety, within the ball raceway, and thus, are intended to remain in clearance relation within the helical grooves of both the screw and the nut. Accordingly, during normal intended use the legs are not contacted by either the nut or the screw, but rather, remain in free floating relation therebetween. However, during use of the ball screw assembly, wear of the screw, nut and balls occurs, thereby resulting in axial and radial lash between the screw and nut. The lash increases over continued use, and as such, over an extended period of time, the legs can eventually come into contact with a helical land of the screw thread. If left unaddressed, continued and ever increasing contact between the legs and the helical land can result in stress fractures within a union region between the leg and the body of the crossover insert, ultimately resulting in the leg breaking away from the body of the crossover insert.